Neptunium behavior in solvent extraction of uranium at Savannah River Plant

The solvent extraction behavior of neptunium in the processing of irradiated natural uranium (Purex process) and irradiated enriched uranium (HM process) at Savannah River was studied in the laboratory. Conditions were demonstrated for extracting neptunium in the first solvent extraction contactor of each process, and two methods were developed for partitioning neptunium from uranium in the HM process. (auth

Plutonium dissolution process

A two-step process for dissolving Pu metal is disclosed in which two steps can be carried out sequentially or simultaneously. Pu metal is exposed to a first mixture of 1.0-1.67 M sulfamic acid and 0.0025-0.1 M fluoride, the mixture having been heated to 45-70 C. The mixture will dissolve a first portion of the Pu metal but leave a portion of the Pu in an oxide residue. Then, a mineral acid and additional fluoride are added to dissolve the residue. Alternatively, nitric acid between 0.05 and 0.067 M is added to the first mixture to dissolve the residue as it is produced. Hydrogen released during the dissolution is diluted with nitrogen

Synthesis of Bimetallic Uranium and Neptunium Complexes of a Binucleating Macrocycle and Determination of the Solid-State Structure by Magnetic Analysis

Syntheses of the bimetallic uranium(III) and neptunium(III) complexes [(UI)2(L)], [(NpI)2(L)], and [{U(BH4)}2(L)] of the Schiff-base pyrrole macrocycles L are described. In the absence of single-crystal structural data, fitting of the variable-temperature solid-state magnetic data allows the prediction of polymeric structures for these compounds in the solid state.JRC.E.6-Actinides researc

Solvation free energy profile of the SCN- ion across the water-1,2-dichloroethane liquid/liquid interface. A computer simulation study

The solvation free energy profile of a single SCN- ion is calculated across the water-1,2-dichloroethane liquid/liquid interface at 298 K by the constraint force method. The obtained results show that the free energy cost of transferring the ion from the aqueous to the organic phase is about 70 kJ/mol, The free energy profile shows a small but clear well at the aqueous side of the interface, in the subsurface region of the water phase, indicating the ability of the SCN- ion to be adsorbed in the close vicinity of the interface. Upon entrance of the SCN- ion to the organic phase a coextraction of the water molecules of its first hydration shell occurs. Accordingly, when it is located at the boundary of the two phases the SCN- ion prefers orientations in which its bulky S atom is located at the aqueous side, and the small N atom, together with its first hydration shell, at the organic side of the interface

Lanthanide-based time-resolved luminescence immunoassays

The sensitive and specific detection of analytes such as proteins in biological samples is critical for a variety of applications, for example disease diagnosis. In immunoassays a signal in response to the concentration of analyte present is generated by use of antibodies labeled with radioisotopes, luminophores, or enzymes. All immunoassays suffer to some extent from the problem of the background signal observed in the absence of analyte, which limits the sensitivity and dynamic range that can be achieved. This is especially the case for homogeneous immunoassays and surface measurements on tissue sections and membranes, which typically have a high background because of sample autofluorescence. One way of minimizing background in immunoassays involves the use of lanthanide chelate labels. Luminescent lanthanide complexes have exceedingly long-lived luminescence in comparison with conventional fluorophores, enabling the short-lived background interferences to be removed via time-gated acquisition and delivering greater assay sensitivity and a broader dynamic range. This review highlights the potential of using lanthanide luminescence to design sensitive and specific immunoassays. Techniques for labeling biomolecules with lanthanide chelate tags are discussed, with aspects of chelate design. Microtitre plate-based heterogeneous and homogeneous assays are reviewed and compared in terms of sensitivity, dynamic range, and convenience. The great potential of surface-based time-resolved imaging techniques for biomolecules on gels, membranes, and tissue sections using lanthanide tracers in proteomics applications is also emphasized

Exotic fish in exotic plantations: a multi-scale approach to understand amphibian occurrence in the mediterranean region

Globally, amphibian populations are threatened by a diverse range of factors including habitat destruction and alteration. Forestry practices have been linked with low diversity and abundance of amphibians. The effect of exotic Eucalyptus spp. plantations on amphibian communities has been studied in a number of biodiversity hotspots, but little is known of its impact in the Mediterranean region. Here, we identify the environmental factors influencing the presence of six species of amphibians (the Caudata Pleurodeles waltl, Salamandra salamandra, Lissotriton boscai, Triturus marmoratus and the anurans Pelobates cultripes and Hyla arborea/meridionalis) occupying 88 ponds. The study was conducted in a Mediterranean landscape dominated by eucalypt plantations alternated with traditional use (agricultural, montados and native forest) at three different scales: local (pond), intermediate (400 metres radius buffer) and broad (1000 metres radius buffer). Using the Akaike Information Criterion for small samples (AICc), we selected the top-ranked models for estimating the probability of occurrence of each species at each spatial scale separately and across all three spatial scales, using a combination of covariates from the different magnitudes. Models with a combination of covariates at the different spatial scales had a stronger support than those at individual scales. The presence of predatory fish in a pond had a strong effect on Caudata presence. Permanent ponds were selected by Hyla arborea/meridionalis over temporary ponds. Species occurrence was not increased by a higher density of streams, but the density of ponds impacted negatively on Lissotriton boscai. The proximity of ponds occupied by their conspecifics had a positive effect on the occurrence of Lissotriton boscai and Pleurodeles waltl. Eucalypt plantations had a negative effect on the occurrence of the newt Lissotriton boscai and anurans Hyla arborea/meridionalis, but had a positive effect on the presence of Salamandra salamandra, while no effect on any of the other species was detected. In conclusion, eucalypts had limited effects on the amphibian community at the intermediate and broad scales, but predatory fish had a major impact when considering all the scales combined. The over-riding importance of introduced fish as a negative impact suggests that forest managers should prevent new fish introductions and eradicate fish from already-occupied ponds whenever possible

Uranium solubility studies during waste evaporation

The liquid waste streams from chemical processing of reactor-irradiated targets and fuel are neutralized with excess NaOH and discharged to mild steel waste tanks for interim storage. To reduce the number of tanks required, and thus the cost of waste storage, the supernate is evaporated to about 70% solids, discharged while hot into clean waste tanks. As the solution cools, solids crystallize from the saturated solution and form a solid layer on the bottom of the tank. The supernate is re-evaporated to concentrate the volume further. Evaporation and crystallization are continued until, for tank 41, the tank is almost filled with crystallized salts. In the DWPF processing scheme, these salts will be redissolved in water and {sup 137}Cs precipitated with sodium tetraphenylborate in the in-tank precipitation facility. The decontaminated supernate is now mixed with cement and stored as a solid monolith; the precipitated Cs and the base-insoluble solids are encapsulated in glass for permanent storage. Questions have been raised about the nuclear safety of these operations, particularly for tank 41, where the waste source was waste from the H-Area fuel processing. One scenario for a potential nuclear accident considers that the salts in tank 41 would dissolve in water, but the enriched uranium solids would not dissolve. The uranium is hypothesized to settle to the bottom of the tank and become concentrated enough to reach a critical mass. A second scenario, promulgated by West Valley, is that uranium would precipitate in the evaporator and form a critical mass in the evaporator. To shed some light on the probable behavior of U in the waste system, the solubility of U in synthetic waste was studied. The results are reported here